The present invention relates to joining and sealing conduits, and, in particular, to joining and sealing conduits of various shapes in areas with a lack of accessibility and visibility.
Conduits, such as ducts, hoses, pipes, tubes and the like are frequently used to transport various fluids, gases or other elements within a structure, such as a vehicle, aircraft or building. Many times the conduits are installed after the structure is partially or totally built, and the conduits must be installed in pieces. The pieces of the conduits then must be joined and sealed after installation.
For example, in the aircraft industry, the environmental control system includes ducts to carry the fluids, gases, air, and the like required to regulate the environment of the aircraft. Typically, the environmental control system ducts are designed and installed after the aircraft is partially or totally built, such that the duct shape must conform to the available space and the ducts must be installed in pieces to avoid structural interferences. As the ducts are installed, nominal one to three inch gaps are generally maintained between the duct segments depending upon the length and material of the duct in order to allow for expansion during operation. Thus, the ducts may be round, elliptical, square, or any other shape that fits in the available space, and the segments of the duct must be joined and sealed in the already congested areas of the aircraft where there is little room to access or view the entire duct joint area.
The conventional manner of joining environmental control system ducts includes bonding elastomeric sheeting, such as flat sheets of silicone impregnated glass, around adjacent portions of the connecting ducts with adhesive, such as Room Temperature Vulcanized (RTV) adhesive. The adhesive must be applied at several locations on the duct system, which is difficult because of the limited space around the duct, the time-sensitive nature of completing the adhesive bond, and the uniqueness of the design of the ducts.
The process of bonding the elastomeric sheeting to join the ducts requires surface preparation, cleaning, multiple supplies, and tools. In addition to the supplies and tools used to apply the sheeting to the ducts, an x-ray machine is also typically used to determine the integrity of the bond between the sheeting and the duct. The x-ray photographs of the joint area reveal where there are voids in the adhesive, uneven application of adhesive, substrate mating pressure, or other issues with the adhesive that may affect the bond between the sheeting and the duct. If the x-rays reveal a problem with the bond, then the installer must remove the sheeting and the adhesive, reapply the adhesive and sheeting, and again x-ray the joint to determine the integrity of the bond. This process must be repeated until the bond between the sheeting and the duct is acceptable.
Once the bond between the sheeting and the duct is acceptable, the elastomeric sheeting is then clamped to the ducts with metal band clamps or tie wraps. The clamps, however, do not provide uniform circumferential pressure to the sheeting covered duct joints, particularly not to the ducts that are square or have some other non-round shape. Thus, when a duct experiences deflection due to internal pressure, the clamp may cause the duct surface to concave, which creates a gap and causes leakage of the elements within the duct. Deflection of the duct also may cause the duct to change shape, which may result in the loosening of the grip of the clamps, a break in the adhesive, and leakage of the elements contained in the ducts. Furthermore, even if the clamps remain tightly in place on the sheeting and ducts, the sharp edges of the clamp may cut into the elastomeric sheeting, particularly as the ducts are subjected to the vibrations, shocks and pressures associated with the operation of an aircraft. Once the clamp cuts into the sheeting, the sheeting will tear and, again, cause leakage of the elements contained in the ducts.
The leaking of the elements contained in the ducts is particularly severe in aircraft that are operated in high humidity or tropical climates because the environmental control system ducts contain high levels of moisture condensation. If the ducts are not completely joined and sealed, the fluid may leak onto electrical systems housed below the ducts and through overhead ceiling panels into the passenger area or body of the aircraft. The moisture release may require a pilot to initiate emergency landing procedures, which includes dumping fuel for a premature landing at the nearest airport.
In order to repair the leaking duct joints, the clamps and sheeting must be removed and the adhesive must be cleaned off of the ducts, which is difficult, time-consuming, and prone to damage the ducts. New adhesive, sheeting and clamps then must be re-applied to the ducts, which is another labor-intensive and time-consuming procedure that is not guaranteed to remedy the problem. In addition, during certain mandatory aircraft maintenance and structural checks, the entire environmental control duct system must be removed and re-installed. After repeated repairs and re-installations, the entire environmental control duct system must be replaced because of the wear and tear on the joint bonding surfaces of the ducts. Therefore, in addition to the time and expense involved in the initial joining and sealing of the ducts, the repairs, re-installation and ultimate replacement is extremely costly because of the human labor and time involved, the loss of flight time for the aircraft, and the cost of replacing the parts of the duct system that cannot be reused after removal.
Thus, there exists a need in the industry for an efficient manner in which to join and seal conduits that have inherent system issues. In particular, there exists a need for an efficient way to join and completely seal conduits of various shapes such that the deflection of the conduit under internal pressure will not cause leakage from the joints, and the joints will not have to be repaired or replaced frequently. Additionally, it would be desirable if the joints may be removed for thorough maintenance checks and reinstalled without an excessive investment of human labor and time, without significant loss of flight time for the aircraft, and without having to replace part or all of the conduit system.
The apparatus and method for joining and sealing conduits of the present invention provide an efficient way to join, seal, and maintain conduits that have various shapes and/or are located in areas that are difficult to view and/or access. The apparatus and method of the present invention also provide an efficient manner in which to join and maintain a continuous seal about the joints of conduits of various shapes, which prevents the deflection of the conduit under internal pressure from causing leakage from the joint. As such, the conduit joints sealed by the apparatus and method of the present invention should have to be repaired less often. Furthermore, the conduits joined and sealed by the apparatus and method of the present invention may be removed for thorough maintenance checks and reinstalled without expending large amounts of human labor, time, and testing, and without additional loss of flight time for the aircraft. Because the apparatus for joining conduits of the present invention may be reused after removal, the conduit system can also be reinstalled without having to replace all of the hardware that forms the conduit joint.
The apparatus for joining and sealing conduits, such as ducts, includes edge trim, a sleeve, and a retaining element. The edge trim is shaped to mount upon and engage an end of a conduit. The edge trim is also shaped to extend at least partially along the outer surface of the conduit near the end of the conduit, and may extend at least partially along the inner surface of the conduit near the end of the conduit. A ridge may extend outwardly from the outer surface of the edge trim, near the end of the conduit. The edge trim may be made of an elastomeric material. Alternatively, the edge trim may be made of silicone. In addition, the edge trim may contain reinforcing material.
The sleeve extends between the conduits and at least partially surrounds the edge trim, including the ridge carried by the edge trim. The sleeve may be made of compressible material, such as elastomeric foam or plastic foam, such that when the retaining element surrounds a portion of the sleeve and the edge trim, the retaining element compresses the sleeve. The sleeve also may have a layer of first elastomer-coated fabric on at least one surface of the sleeve, such as the surface that faces the edge trim. Additionally, a layer of material, at least a portion of which has a lower coefficient of friction than the layer of first elastomer-coated fabric may be located on the side of the sleeve that faces the retaining element contact area to facilitate movement of the retaining element over the sleeve at least initially. The portion of the material having a lower coefficient of friction than the layer of first elastomer-coated fabric may be a second elastomer-coated fabric.
In one embodiment, the sleeve has a core, a first layer and a second layer. The core region of the sleeve has an inner surface and an outer surface. The core region may be made of plastic foam or an elastomeric foam. The first layer of the sleeve is bonded to the inner surface of the core. The first layer may be an elastomer-coated fabric. The second layer of the sleeve is bonded to the outer surface of the core and has a lower coefficient of friction than the first layer. The first and second layers may be longer than the core, such that the first and second layers may be bonded together beyond the ends of the core. The sleeve also may include a third layer bonded to the second layer proximate a medial portion of the sleeve for reinforcement of that portion of the sleeve extending between the conduits to prevent the sleeve from ballooning due to pressure inside the conduit during operation of the conduit.
According to the present invention, the method for fabricating the sleeve may include providing the sleeve core having an inner surface and an outer surface, and positioning uncured elastomer-coated fabric that is longer than the sleeve core on the inner and outer surfaces of the sleeve core. A porous material is placed between the fabric portions that extend beyond the sleeve core to ensure that the fabric portions will not bond, and to allow vapors to escape during curing of the fabric to the sleeve core. The porous material is removed after curing, and the fabric portions that extend beyond the sleeve are then bonded together. The porous material may be made of a breather material and a release film. The method of fabricating the sleeve may also position a band of uncured elastomer-coated fabric over the fabric that is positioned on the outer surface of the sleeve core, typically over a medial portion of the sleeve core, prior to curing the fabric to the sleeve core. The uncured elastomer-coated fabric may be silicone coated fabric.
The retaining element surrounds a portion of the sleeve and the edge trim to hold the sleeve in position with respect to the edge trim. The retaining element is generally made of a rigid material and may have a first portion with a first circumference and a second portion with a second circumference. The first inner circumference may be smaller than the second inner circumference and the retaining element may be placed on the sleeve such that the larger second portion is closest to the end of the conduit. If the edge trim has a ridge, the first portion of the retaining element may surround a portion of the sleeve on the side of the ridge that is opposite the end of the conduit and the second portion of the retaining element may be near the ridge so as to sandwich a portion of the sleeve therebetween.
In one embodiment of the present invention, the retaining element also may have an outwardly extending support having at least one aperture. A tie member may extend through the aperture of the retaining element to lock the retaining element to another retaining element mounted upon an end of another conduit.
The method of joining and sealing conduits of the present invention includes mounting the edge trim and a retaining element upon an end of a conduit, such that the retaining element is further from the end of the conduit than the ridge carried by the edge trim. The edge trim also may be bonded to the conduit during the mounting of the edge trim. The method also includes extending a sleeve between the conduits, such that one end of the sleeve covers the ridge on the edge trim, and sliding the retaining element over the sleeve and toward the ridge, such that a portion of the sleeve is sandwiched between the retaining element and the ridge.
Sliding the retaining element over the sleeve generally compresses that portion of the sleeve that underlies the retaining element and displaces the sleeve material to expand on either side of the retaining element. In sliding the retaining element, the retaining element is generally positioned such that the retaining element is prevented from moving past the ridge toward the end of the conduit and at least partially restrained from moving away from the ridge due to the displaced material on the side of the retaining element opposite the ridge. In one embodiment of the present invention, the method also includes the option of attaching at least one tie member to the retaining element to lock the retaining element to another retaining element mounted upon an end of another conduit.
As a result of its construction and the corresponding installation method, the edge trim, sleeve and retaining element continue to provide a tight, leak-proof seal about the conduits as the shape of the conduits experience deflection due to internal pressure. Moreover, the apparatus and method of the present invention provide an efficient technique to couple conduits, while permitting removal for inspection or the like and subsequent reinstallation, particularly in areas that are difficult to view and/or access.